Cellulose and hemicellulose of plant cell walls are an important energy source for ruminants but are present in a matrix with undegradable lignin. The nutritional value of lignocellulosic biomass can potentially be increased by fungal treatment. Researchers of the Animal Nutrition Group and Laboratory of Plant Breeding of Wageningen University authored a comprehensive review describing the state-of-the-art use of white rot fungi, which can selectively degrade lignin and ultimately aid in increasing the utilisation of lignocellulosic biomass in ruminant nutrition.
Ruminants are specialists in degrading carbohydrates in plant material. In plant cell walls, the carbohydrates, cellulose and hemicellulose, are bound to lignin and form the lignocellulosic complex. Lignin cannot be degraded in the anaerobic environment of the rumen, and can be considered as a blockage for rumen microbes to reach the carbohydrates. This means that a pretreatment of lignocellulosic material is necessary to improve its nutritional value.
Instead of using chemical or physical pretreatments, which are expensive and can result in toxic waste streams, we propose a biological pretreatment. Biological pretreatments use highly selective lignin degrading white rot fungi. An overview of literature describing fungal pretreatments is provided in this review.
Fungal treatment starts with colonization of the substrate with a lignin degrading fungus. During colonization, enzymes, radicals and other small compounds will be produced by the fungus to break down lignin. The mechanisms on how these fungi degrade lignin are not fully understood, but fungal strain, the origin of lignocellulose and culture conditions have a major effect on the process.
Generally, Ceriporiopsis subvermispora and Pleurotus eryngii are the most effective fungi to improve the nutritional value of biomass for ruminant nutrition, as found in in vitro and in some in vivo studies. Up to now fungal treatment has not been used in practice due to the long treatment time needed and the fact that fungi in some cases also consume carbohydrates, decreasing the yield. The authors suggest to focus on culture conditions and gene expressions to optimize the process. Optimized fungal treatments should be tested in vivo to understand the long term effects on the animals and product quality.
This research was supported by the Dutch Technology Foundation (STW), which is part of the Netherlands Organization for Scientific Research (NWO), which is partly funded by the Dutch Ministry of Economic Affairs. This project (11611) was co-sponsored by Agrifirm, Purac, DSM, Den Ouden, Hofmans and Wageningen University.
The review has been published in Biotechnology Advances and is available via the this link.